Symptom: ThreadLock::writeLock blocks after second call.
Problem: Certain implementations of pthreads read write
locks default initialization will block on recursive
calls to 'pthread_rwlock_wrlock'.
Platform: 'pthread_rwlock_wrlock' in libc6 v2.3.5-6 as
distributed with Debian GNU/Linux is NOT recursive.
This applies both to LinuxThreads and NPTL.
1. fix NPTL.
2. write a workaround using mutexes.
Low priority, I think...